High performance refrigerator having dual evaporator

ABSTRACT

A high performance refrigerator includes a cabinet with a unitary refrigerated interior and a refrigeration fluid circuit having first and second evaporators located within the cabinet and separated from the refrigerated interior by respective first and second evaporator covers. The refrigerator also includes a first damper controlling flow between the first evaporator and the refrigerated interior, and a second damper controlling flow between the second evaporator and the refrigerated interior. A controller directs the refrigerator to operate a three-way valve in the refrigeration fluid circuit so as to direct refrigerant to only one of the evaporators when the other requires defrosting. Both evaporators may be used to remove heat from the unitary refrigerated interior during an initial cooling or immediately after the cabinet is opened.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the priority benefit of U.S. Provisional Patent Application No. 61/548,800 (pending), filed Oct. 19, 2011, the disclosure of which is hereby incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates generally to refrigerators or freezers and, more particularly, to refrigeration systems for use with high performance blood bank refrigerators or plasma freezers.

BACKGROUND OF THE INVENTION

Refrigeration systems are known for use with laboratory refrigerators and freezers of the type known as “high performance refrigerators,” which are used to cool their interior storage spaces to relative low temperatures such as about −30° C. or lower, for example. These high performance refrigerators are used to store blood and/or plasma, in one example.

Known refrigeration systems of this type include a single loop circulating a refrigerant. The system transfers energy (i.e., heat) from the refrigerant to the surrounding environment through a condenser, and the system transfers heat energy to the refrigerant from the cooled space (e.g., a cabinet interior) through an evaporator. The refrigerant is selected to vaporize and condense at a selected temperature close to the desired temperature for the cooled space, such that the refrigeration system can maintain the cooled space near that selected temperature during operation.

One common problem with known refrigeration systems is that the evaporator includes coils that tend to produce and accumulate frost along the outer surface if any moisture is ambient within the cooled space. If enough frost accumulation occurs, the ability of the evaporator to remove heat from the cooled space is detrimentally impacted. Consequently, known refrigeration systems require a defrost cycle where the evaporator coils are heated to remove the frost. This defrost cycle may be a manual defrost or an automatic defrost, but both types of defrost cycles are undesirable for various reasons.

In a manual defrost cycle, all of the products stored in the cabinet are removed and the cooled space is left exposed to the ambient environment to heat up the evaporator coils and melt the frost. This cycle is undesirable because the products stored in the cabinet need to be stored in an alternative refrigerator for the duration of the defrost cycle, and also because the melting process can produce a significant amount of moisture that needs to be removed from the cabinet. In an automatic defrost cycle, the evaporator coils are rapidly heated by a local heating unit or hot gas flow to remove the frost, which is collected by a trough and delivered out of the cooled space. The cooled space necessarily undergoes a temperature spike during this automatic defrost cycle, which can jeopardize the products stored in the cabinet.

There is a need, therefore, for a refrigerator that substantially minimizes or eliminates a temperature spike within the cooled space during a defrost cycle.

SUMMARY OF THE INVENTION

In one embodiment, a refrigerator includes a cabinet with a unitary refrigerated interior and a refrigeration fluid circuit for circulating a refrigerant. The refrigeration fluid circuit includes a compressor, a condenser, an expansion device, a first evaporator located within the cabinet, a second evaporator located within the cabinet, and a three-way valve enabling selective communication of the refrigerant through one or both of the first and second evaporators. The first evaporator includes a first evaporator coil, a first evaporator fan producing air flow through the first evaporator coil, and a first evaporator cover separating a first evaporator compartment from the refrigerated interior. The second evaporator includes a second evaporator coil, a second evaporator fan producing air flow through the second evaporator coil, and a second evaporator cover separating a second evaporator compartment from the refrigerated interior. The refrigerator also includes at least one first damper that opens to permit air circulation through the first evaporator cover from the refrigerated interior through the first evaporator. The refrigerator further includes at least one second damper that opens to permit air circulation through the second evaporator cover from the refrigerated interior through the second evaporator. The three-way valve directs refrigerant into only one of the evaporators when the other evaporator requires defrosting.

The refrigerator further includes a controller operable to command the refrigerator to perform a series of steps defining a defrost cycle when the first evaporator requires defrosting. In this regard, the first evaporator includes a first defrost heater. The series of steps includes directing refrigerant with the three-way valve through only the second evaporator, removing heat from the refrigerated interior with the second evaporator, stopping operation of the first evaporator fan, closing the at least one first damper to isolate the first evaporator from the refrigerated interior, and starting operation of the first defrost heater. The controller is also operable to command the refrigerator to perform a second series of steps when the second evaporator requires defrosting. The second series of steps includes directing refrigerant with the three-way valve through only the first evaporator, removing heat from the refrigerated interior with the first evaporator, stopping operation of the second evaporator fan, closing the at least one second damper to isolate the second evaporator from the refrigerated interior, and starting operation of the second defrost heater. During periods of initial cooling or immediately after the cabinet is opened, the controller may instruct the three-way valve to direct refrigerant to both evaporators so that both evaporators may simultaneously remove heat from the refrigerated interior.

In one aspect, the at least one first damper includes two first damper portions, one of which permits air flow into the first evaporator from the refrigerated interior when open, the other of which permits air flow from the first evaporator into the refrigerated interior when open. Additionally, the at least one second damper includes two second damper portions, one of which permits air flow into the second evaporator from the refrigerated interior when open, the other of which permits air flow from the second evaporator into the refrigerated interior when open.

In another embodiment of the invention, a method of operating a refrigerator is provided, the refrigerator including a cabinet with a unitary refrigerated interior and a refrigeration fluid circuit. The refrigeration fluid circuit includes a compressor, a condenser, a first evaporator located within the cabinet and having a first evaporator fan and a first defrost heater, a second evaporator located within the cabinet and having a second evaporator fan and a second defrost heater, and a three-way valve enabling selective communication of a refrigerant between the compressor/condenser and one or both of the evaporators. The refrigerator also includes first and second dampers configured to respectively isolate the first and second evaporators from the refrigerated interior. When the first evaporator requires defrosting, the method includes directing refrigerant with the three-way valve through only the second evaporator, removing heat from the refrigerated interior with the second evaporator, stopping operation of the first evaporator fan, closing the first damper to isolate the first evaporator from the refrigerated interior, and starting operation of the first defrost heater.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with a general description of the invention given above, and the detailed description of the embodiment given below, serve to explain the principles of the invention.

FIG. 1 is a perspective view of a refrigerator including a dual evaporator according to an exemplary embodiment.

FIG. 2 is a schematic representation of the refrigeration fluid circuit used with the refrigerator of FIG. 1.

FIG. 3 is a perspective view of an evaporator cover (shown in phantom) and dampers used with the refrigerator of FIG. 1.

FIG. 4 is a perspective view of one of the evaporators used with the refrigerator of FIG. 1, with some of the side panels shown in phantom to reveal interior elements.

FIG. 5 is a cross-sectional top view of the refrigerator of FIG. 1 along line 5-5, with the dampers in a closed position.

FIG. 6A is a cross-sectional side view of the refrigerator of FIG. 5 along line 6A-6A, with the dampers in a closed position.

FIG. 6B is a cross-sectional side view of the refrigerator of FIG. 5 along line 6A-6A, with the dampers in an open position.

FIG. 7A is a cross-sectional side view of the refrigerator of FIG. 5 along line 7A-7A, with the dampers in a closed position.

FIG. 7B is a cross-sectional side view of the refrigerator of FIG. 5 along line 7A-7A, with the dampers in an open position.

FIG. 8 is a schematic diagram of the controller and damper drive elements used with the refrigerator of FIG. 1.

FIG. 9 is a schematic flowchart illustrating an operational sequence of a controller associated with the refrigerator of FIG. 1.

DETAILED DESCRIPTION

With reference to the figures, and more specifically to FIG. 1, an exemplary high performance refrigerator 10 according to one embodiment of the present invention is illustrated. Although the terms “high performance refrigerator” and “refrigerator” are used throughout the specification, it will be understood that the invention encompasses any type of cooling device, including a refrigerator that comprises a freezer. The refrigerator of FIG. 1 includes a cabinet 12 for storing items that require cooling to temperatures of about −30° C. or lower, for example. The cabinet 12 includes a cabinet housing 14 defining a generally rectangular cross-section and a door 16 providing access into an interior 18 of the cabinet 12. The cabinet 12 supports one or more components that jointly define a single-stage refrigeration fluid circuit 20 (FIG. 2) that thermally interacts with the air within the cabinet 12 to cool the interior 18 thereof. In this regard, the refrigeration fluid circuit 20 described in further detail below interacts with warmed air in the interior 18 and cools this air to maintain a desired cold temperature in the cabinet 12.

With reference to FIG. 2, details of the exemplary refrigeration fluid circuit 20 are illustrated. The refrigeration fluid circuit 20 includes, in sequence, a compressor 22, a condenser 24, a filter/dryer 26, a three-way valve 28, an expansion device 30, a first evaporator 32 and a second evaporator 34 in parallel, and a suction/accumulator 36. Each of these elements of the refrigeration fluid circuit 20 is coupled by piping or tubing 38 configured to circulate the refrigerant 40 passing through the refrigeration fluid circuit 20. A plurality of sensors S₁ through S₇ are arranged to sense different conditions of the fluid circuit 20 and/or properties of the refrigerant (shown by arrows 40) at various locations within the fluid circuit 20. Each of these sensors S₁ through S₇ is operatively coupled to a controller 50 accessible through a controller interface 52, which permits controlling of the operation of the fluid circuit 20. It will be appreciated that more or fewer sensors may be provided than the number shown in the exemplary embodiment of the fluid circuit 20.

The refrigeration fluid circuit 20 is configured to circulate the refrigerant 40 between the condenser 24 and the first and second evaporators 32, 34. Generally speaking, heat energy in the refrigerant 40 is transferred to ambient air outside the cabinet 12 at the condenser 24. Heat energy is removed from the interior 18 of the cabinet 12 and transferred to the refrigerant 40 at the first and second evaporators 32, 34. Thus, circulating the refrigerant 40 through the fluid circuit 20 continuously removes heat energy from the interior 18 to maintain a desired internal temperature, such as, for example −30° C.

The refrigerant 40 enters the compressor 22 in a vaporized state and is compressed to a higher pressure and higher temperature gas in the compressor 22. The fluid circuit 20 of this exemplary embodiment also includes an oil loop 54 for lubricating the compressor 22. Specifically, the oil loop 54 includes an oil separator 56 in fluid communication with piping 38 downstream of the compressor 22 and an oil return line 58 directing oil back into the compressor 22. It will be understood that the oil loop 54 may be omitted in some embodiments of the fluid circuit 20.

Upon leaving the compressor 22, the vaporized refrigerant 40 travels to the condenser 24. A fan 60 controlled by the control interface 52 directs ambient air across the condenser 24 and through a filter 62 so as to facilitate the transfer of heat from the refrigerant 40 to the surrounding environment. The air flow through the condenser 24 is shown by arrows in FIG. 2. The refrigerant 40 condenses within the condenser 24 as a result of this heat transfer. The liquid-phase refrigerant 40 then passes through the filter/dryer 26 and the three-way valve 28, then into the expansion device 30. In this embodiment, the expansion device 30 is in the form of a first capillary tube 30 a leading to the first evaporator 32 and a second capillary tube 30 b leading to the second evaporator 34, although it is contemplated that it could instead take another form such as, and without limitation, corresponding expansion valves (not shown). Additionally, the expansion device 30 could alternatively be located upstream of the three-way valve 28 in other embodiments within the scope of the invention. The expansion device 30 causes a pressure drop in the refrigerant 40 immediately before the refrigerant 40 enters the first and second evaporators 32, 34.

In each of the first and second evaporators 32, 34, the refrigerant 40 receives heat from the interior 18 through a plurality of evaporator coils (not shown in FIG. 2). A first evaporator fan 64 controlled by the control interface 52 forces air flow from the interior 18 of the cabinet 12 through the evaporator coils of the first evaporator 32 when first and second dampers 66, 68 are opened. Similarly, a second evaporator fan 70 controlled by the control interface 52 forces air flow from the interior 18 of the cabinet 12 through the evaporator coils of the second evaporator 34 when third and fourth dampers 72, 74 are opened. The first, second, third, and fourth dampers 66, 68, 72, 74 are also controlled by the control interface 52, which is described in further detail with reference to FIG. 9, below. By virtue of the lowered pressure and the heat transfer from the cabinet 12, the refrigerant 40 vaporizes within the first and second evaporators 32, 34. The vaporized refrigerant 40 is then directed to the suction/accumulator device 36. The suction/accumulator 36 passes the refrigerant 40 in gaseous form to the compressor 22, while also accumulating excessive amounts of the refrigerant 40 in liquid form and feeding it to the compressor 22 at a controlled rate.

The refrigerant 40 used in the refrigeration fluid circuit 20 may be chosen based on several factors, including the expected operating temperature within the cabinet 12 and the boiling point and other characteristics of the refrigerant 40. For example, in refrigerators with an expected cabinet temperature of about −30° C., an exemplary refrigerant 40 suitable for the presently described embodiment includes refrigerants commercially available under the respective designations R404A. Moreover, in specific embodiments, the refrigerant 40 may be combined with an oil to facilitate lubrication of the compressor 22. For example, and without limitation, the refrigerant 40 may be combined with Mobil EAL Arctic 32 oil. It will be understood that the precise arrangement of the components illustrated in the figures is intended to be merely exemplary rather than limiting.

With reference to FIGS. 3-7B and in particular FIG. 3, the refrigerator 10 includes an insulated cover defined by a first evaporator cover 76 and a second evaporator cover 78 that collectively divide the interior 18 of the cabinet 12 into a first evaporator compartment 80, a second evaporator compartment 82, and a refrigerated interior portion 84. The first and second evaporator covers 76, 78 are coupled to one or more of the top wall 86, the side walls 88 (including a rear wall 88), and/or the bottom wall 90 collectively defining the cabinet housing 14. More particularly, the first evaporator cover 76 is coupled to the top wall 86 and the side walls 88 of the cabinet housing 14 to thermally isolate the evaporator compartments 80, 82 from the heat energy within the interior 18 as that heat energy rises within the interior 18 of the cabinet 12. The first evaporator cover 76 includes a vertical panel portion 76 a extending downwardly from the top wall 86 of the cabinet housing 14 and a horizontal panel portion 76 b extending between the vertical panel portion 76 a and the side walls 88 of the cabinet housing 14. Similarly, the second evaporator cover 78 includes a vertical panel portion 78 a extending downwardly from the top wall 86 and a horizontal panel portion 78 b extending between the vertical panel portion 78 a and the side walls 88. The vertical panel portions 76 a, 78 a and the horizontal panel portions 76 b, 78 b are formed from one or more thermally insulating panels, such as a hollow vacuum insulated panel (shown in FIG. 4). It will be understood that other types of insulating panels may be used in other embodiments of the invention, including but not limited to foam-based panels.

As shown in FIG. 3, the first evaporator compartment 80 is defined as a generally rectilinear space by the corresponding vertical panel portion 76 a, the horizontal panel portion 76 b, the side walls 88, the top wall 86, and an insulated divider wall 92 located between the first evaporator compartment 80 and the second evaporator compartment 82. The first evaporator 32 mounts into a first sub-divider panel 94 located generally centrally within the first evaporator compartment 80 so as to divide the first evaporator compartment 80 into an inlet side 96 and an outlet side 98.

In a similar manner, the second evaporator compartment 82 is defined as a generally rectilinear space by the corresponding vertical panel portion 78 a, the horizontal panel portion 78 b, the side walls 88, the top wall 86, and the insulated divider wall 92. The second evaporator 34 mounts into a second sub-divider panel 100 located generally centrally within the second evaporator compartment 82 so as to divide the second evaporator compartment 82 into an inlet side 102 and an outlet side 104. The divider wall 92 and each of the first and second sub-divider panels 94, 100 are formed from a vacuum insulated panel or a foam-based insulated panel in this embodiment, although it will be understood that other types of insulated panels may also be used in other embodiments.

The horizontal panel portion 76 b of the first evaporator cover 76 includes an inlet aperture 106 on the inlet side 96 of the first sub-divider panel 94 and an outlet aperture 108 on the outlet side 98 of the first sub-divider panel 94. The first damper 66 includes an insulated panel that is operable to rotate to open or close flow through the inlet aperture 106 between the inlet side 96 and the refrigerated interior 18 of the cabinet 12. Similarly, the second damper 68 includes an insulated panel that is operable to rotate to open or close flow through the outlet aperture 108 between the outlet side 98 and the refrigerated interior 18 of the cabinet 12. Thus, the first and second dampers 66, 68 may be operated as respective portions of a first damper assembly to enable flow through the first evaporator 32.

The horizontal panel portion 78 b of the second evaporator cover 78 also includes an inlet aperture 110 on the inlet side 102 of the second sub-divider panel 100 and an outlet aperture 112 on the outlet side 104 of the second sub-divider panel 100. The third damper 72 includes an insulated panel that is operable to rotate to open or close flow through the inlet aperture 110 between the inlet side 102 and the refrigerated interior 18 of the cabinet 12. Similarly, the fourth damper 74 includes an insulated panel that is operable to rotate to open or close flow through the outlet aperture 112 between the outlet side 104 and the refrigerated interior 18 of the cabinet 12. To this end, the third and fourth dampers 72, 74 may be operated as respective portions of a second damper assembly to enable flow through the second evaporator 34.

Also shown in FIG. 3, the first and second dampers 66, 68 are operatively connected to a first damper drive mechanism 120 such as respective first and second servo motors 122, 124 and first and second drive shafts 126, 128. The control and operation of the first damper drive mechanism 120 is further described in detail with reference to FIG. 8 below. It will be understood that the first and second drive shafts 126, 128 may be connected by a conventional drive linkage (not shown) in some embodiments so that only a single servo motor would be required to open and close the first and second dampers 66, 68. In this regard, the first and second dampers 66, 68 are typically opened (or closed) simultaneously so that flow is enabled through the first evaporator compartment 80 and the first evaporator 32.

Similarly, the third and fourth dampers 72, 74 are operatively connected to a second damper drive mechanism 130 such as respective third and fourth servo motors 132, 134 and third and fourth drive shafts 136, 138. The control and operation of the second damper drive mechanism 130 is further described in detail with reference to FIG. 8 below. It will be understood that the third and fourth drive shafts 136, 138 may be connected by a conventional drive linkage (not shown) in some embodiments so that only a single servo motor would be required to open and close the third and fourth dampers 72, 74. In this regard, the third and fourth dampers 72, 74 are typically opened (or closed) simultaneously so that flow is enabled through the second evaporator compartment 82 and the second evaporator 34.

Turning to FIG. 4, the first and second evaporators 32, 34 are shown in further detail. To this end, the first evaporator 32 includes a first evaporator housing 140 enclosing a first evaporator coil 142 extending in a serpentine manner across a width of the first evaporator 32. The first evaporator coil 142 is operatively connected to the piping 38 of the refrigeration fluid circuit 20, which carries liquid-phase refrigerant to the first evaporator coil 142 and removes vaporized and any remaining liquid-phase refrigerant from the first evaporator coil 142. The first evaporator fan 64 is mounted along the first evaporator housing 140 at the inlet side 96 of the first evaporator compartment 80 so as to actuate air flow through the first evaporator housing 140 and through the first evaporator coil 142. After flowing through the first evaporator coil 142, cooled air exits the first evaporator housing 140 and enters the outlet side 98 of the first evaporator compartment 80.

The first evaporator 32 also includes a first defrost heater 144 for removing frost build up on the first evaporator coil 142 as needed or on a regular basis. The first defrost heater 144 is shown mounted adjacent to the first evaporator coil 142 in FIGS. 4 and 6A-7B, but it will be appreciated that the first defrost heater 144 may be mounted anywhere within the first evaporator housing 140. The first defrost heater 144 is operated by the controller 50 and the control interface 52 previously described with reference to FIG. 2 to heat up the first evaporator coil 142 and melt any frost. The first evaporator housing 140 further includes a first drip pan 146 located below the first evaporator coil 142 and configured to collect and dispose of melted frost to a location outside the refrigerator 10. In this regard, the first drip pan 146 is generally angled from a horizontal orientation so that moisture dripping from the first evaporator coil 142 automatically flows to a moisture outlet (not shown).

In a similar manner, the second evaporator 34 includes a second evaporator housing 150 enclosing a second evaporator coil 152 extending in a serpentine manner across a width of the second evaporator 34. The second evaporator coil 152 is operatively connected to the piping 38 of the refrigeration fluid circuit 20, which carries liquid-phase refrigerant to the second evaporator coil 152 and removes vaporized and any remaining liquid-phase refrigerant from the second evaporator coil 152. The second evaporator fan 70 is mounted along the second evaporator housing 150 and generates air flow from the inlet side 102 of the second evaporator compartment 82 through the second evaporator coil 152 and to the outlet side 104 of the second evaporator compartment 82. The second evaporator 34 also includes a second defrost heater 154 for removing frost build up on the second evaporator coil 152 as needed or on a regular basis, and a second drip pan 156 located below the second evaporator coil 152 and configured to collect and dispose of melted frost to a location outside the refrigerator 10. The second evaporator 34 is generally identical in construction to the first evaporator 32, and therefore further explanation is unnecessary.

As shown in FIG. 5, the first and second evaporator compartments 80, 82 are spaced rearward from the door 16 in this embodiment of the refrigerator. FIG. 5 also more clearly illustrates how the divider wall 92 and the first and second sub-divider panels 94, 100 split the first and second evaporator compartments 80, 82. The first and second evaporators 32, 34 are shown in generally the same orientation on FIGS. 4 and 5. It will be understood that the orientation of one or both of the evaporators 32, 34 could be reversed or otherwise modified in other embodiments within the scope of the invention.

With reference to FIGS. 6A-7B, the refrigerator 10 further includes an upper compartment 160 located above the top wall 86 of the cabinet housing 14. The upper compartment 160 contains elements of the refrigeration fluid circuit 20 other than the evaporators 32, 34 (e.g., the compressor 22, the condenser 24, etc.), thereby removing most of the space-using or heat generating components from the interior 18 of the cabinet 12. These other elements located within the upper compartment 160 are not shown in FIGS. 6A-7B, although they are schematically shown in FIG. 2. The piping 38 for the refrigerant 40 extends through the top wall 86 to deliver refrigerant 40 between the components in the upper compartment 160 and the first and second evaporators 32, 34 in the cabinet 12.

FIGS. 6A-7B also illustrate multiple operating states for the refrigerator 10. More particularly, in FIG. 6A the first and second dampers 66, 68 are closed, which thermally isolates the first evaporator compartment 80 from the refrigerated portion 84. The first evaporator fan 64 is generally inactive when the first and second dampers 66, 68 are closed because air cannot be circulated into and out of the first evaporator compartment 80. The first defrost heater 144 is only operated in this operational state of the refrigerator 10 so that substantially all of the heat energy generated by the first defrost heater 144 remains within the first evaporator compartment 80 during a defrost cycle or process. To this end, the temperature spike within the refrigerated portion 84 of the interior 18 is reduced or eliminated during the defrost cycle. In contrast, the first and second dampers 66, 68 are open in FIG. 6B so that air from the refrigerated portion 84 may flow through the first evaporator 32 and the first evaporator coil 142 for cooling. The air flow actuated by the first evaporator fan 64 is schematically shown in FIG. 6B by arrows 162. Thus, relatively warm air enters the first evaporator compartment 80 through the first inlet aperture 106 and relatively cold air exits the first evaporator compartment 80 through the first outlet aperture 108 in this operating state of the refrigerator 10.

Similarly, in FIG. 7A the third and fourth dampers 72, 74 are closed, which thermally isolates the second evaporator compartment 82 from the refrigerated portion 84. The second evaporator fan 70 is generally inactive when the third and fourth dampers 72, 74 are closed because air cannot be circulated into and out of the second evaporator compartment 82. The second defrost heater 154 is only operated in this operational state of the refrigerator 10 so that substantially all of the heat energy generated by the second defrost heater 154 remains within the second evaporator compartment 82 during a defrost cycle or process. To this end, the temperature spike within the refrigerated portion 84 of the interior 18 is reduced or eliminated during the defrost cycle. In contrast, the third and fourth dampers 72, 74 are open in FIG. 7B so that air from the refrigerated portion 84 may flow through the second evaporator 34 and the second evaporator coil 152 for cooling. The air flow actuated by the second evaporator fan 70 is schematically shown in FIG. 7B by arrows 164. Thus, relatively warm air enters the second evaporator compartment 82 through the second inlet aperture 110 and relatively cold air exits the second evaporator compartment 82 through the second outlet aperture 112 in this operating state of the refrigerator 10.

FIG. 8 schematically illustrates the control and actuation mechanisms for the first, second, third, and fourth dampers 66, 68, 72, 74. More specifically, the dampers 66, 68, 72, 74 are connected to the corresponding first and second damper drive mechanisms 120, 130, which are coupled to the controller 50. As understood in the art, the controller 50 may include at least one central processing unit (“CPU”) coupled to a memory. Each CPU is typically implemented in hardware using circuit logic disposed on one or more physical integrated circuit devices or chips. Each CPU may be one or more microprocessors, micro-controllers, field programmable gate arrays, or ASICs, while memory may include random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, and/or another digital storage medium, and also typically implemented using circuit logic disposed on one or more physical integrated circuit devices, or chips. As such, memory may be considered to include memory storage physically located elsewhere in the refrigerator 10, e.g., any cache memory in the at least one CPU, as well as any storage capacity used as a virtual memory, e.g., as stored on a mass storage device such as a hard disk drive, another computing system, a network storage device (e.g., a tape drive), or another network device coupled to the controller 50 through at least one network interface by way of at least one network. The computing system, in specific embodiments, is a computer, computer system, computing device, server, disk array, or programmable device such as a multi-user computer, a single-user computer, a handheld computing device, a networked device (including a computer in a cluster configuration), a mobile telecommunications device, a video game console (or other gaming system), etc. The controller 50 includes at least one serial interface to communicate serially with an external device, such as the damper drive mechanisms 120, 130, for example. Thus, the controller 50 functions to actuate operation of the damper drive mechanisms 120, 130.

As previously described, the damper drive mechanisms 120, 130 may include one or more servo motors 122, 124, 132, 134 connected to the dampers 66, 68, 72, 74 via corresponding drive shafts 126, 128, 136, 138. However, the damper drive mechanisms 120, 130 may include other types of actuation mechanisms and devices in other embodiments. For example, the damper drive mechanisms 120, 130 may be hydraulically driven, pneumatically driven, or mechanically driven such as by various types of motors. The damper drive mechanisms 120, 130 may be configured to rotate the dampers 66, 68, 72, 74 between open and closed positions as shown in the illustrated embodiment, but it will be understood that the damper drive mechanisms 120, 130 may alternatively slide or otherwise move the dampers 66, 68, 72, 74 in non-rotational manners as well.

An exemplary operation of the refrigerator 10 is shown schematically in the flowchart of FIG. 9. In this regard, the controller 50 is operable to command the refrigerator 10 to execute the steps of the method 200 shown in that Figure. To this end, the controller 50 determines whether a defrost cycle is necessary for the first evaporator 32 at step 202. For example, in a time-based defrost cycle, the controller 50 at step 202 determines whether a predetermined amount of time has elapsed since the most recent defrost cycle of the first evaporator 32. If so, then the controller 50 begins the defrost cycle for the first evaporator 32 at step 204. If not, then the controller 50 moves to step 218 to check whether the second evaporator 34 requires a defrost cycle, as described in further detail below. In one example, the refrigerator 10 may defrost every six hours, in which case the predetermined amount of time would be six hours. Alternatively, the controller 50 may be operable to perform adaptive defrosts that are spaced by varying amounts of time depending on operational characteristics measured between defrost cycles, as described in further detail below.

Returning to FIG. 9, when a defrost cycle is required to remove frost build up from the first evaporator coil 142, the controller 50 actuates the three-way valve 28 to direct refrigerant 40 to only the second evaporator 34 at step 204. In this regard, the controller 50 continues to operate the second evaporator 34 at step 206 to continue cooling the interior 18 of the cabinet 12 while the first evaporator 32 is defrosted. Next, the controller 50 stops operation of the first evaporator fan 64 at step 208. The controller 50 then closes the first and second dampers 66, 68 (i.e., the first damper assembly) at step 210 to thermally isolate the first evaporator compartment 80 from the refrigerated portion 84 of the cabinet 12. These steps stop refrigerant flow through the first evaporator 32 and also stop air flow through the first evaporator 32. With the first evaporator compartment 80 thermally isolated from the remainder of the cabinet 12, the controller 50 starts operation of the first defrost heater 144 at step 212. The first defrost heater 144 warms the first evaporator 32 and the first evaporator coil 142 to melt frost and cause the moisture to drip onto the first drip pan 146 for removal from the first evaporator 32. The operational state of the refrigerator 10 at this point is shown in FIG. 6A.

One of the sensors S₃ connected to the first evaporator 32 may be configured to measure the temperature of the first evaporator 32. Once the controller 50 determines that the first evaporator 32 has been heated to a first target temperature above the freezing point of water (0° C.) for a sufficient time to melt frost build up on the first evaporator coil 142, the controller 50 stops the first defrost heater 144 at step 214 and allows for a set period of “drip time” in which additional moisture drips off the first evaporator coil 142 into the first drip pan 146. In one example, this first target temperature may be about 10° C. After this “drip time” has occurred, the controller 50 directs refrigerant 40 with the three-way valve 28 through both of the first and second evaporators 32, 34 again at step 216, thereby cooling the first evaporator compartment 80. The first evaporator 32 may then be used as normally shown in FIG. 6B by opening the first and second dampers 66, 68 and starting the first evaporator fan 64. As a result of the first evaporator cover 76, the defrost cycle does not cause a significant temperature spike within the refrigerated interior 18 of the cabinet 12, and the refrigerator 10 therefore is advantageous over conventional refrigerator designs.

Returning to step 218, the controller 50 determines whether a defrost cycle is necessary for the second evaporator 34. For example, in a time-based defrost cycle, the controller 50 at step 218 determines whether a predetermined amount of time has elapsed since the most recent defrost cycle of the second evaporator 34. If so, then the controller 50 begins the defrost cycle for the second evaporator 34 at step 220. If not, then the controller 50 returns to step 202 and continues to wait and periodically check to see if the predetermined amount of time has elapsed for either the first evaporator 32 or the second evaporator 34. As described above with respect to a time-based defrost cycle, the refrigerator 10 may defrost each evaporator 32, 34 every six hours, in which case the predetermined amount of time would be six hours. Alternatively, the controller 50 may be operable to perform adaptive defrosts that are spaced by varying amounts of time depending on operational characteristics measured between defrost cycles.

When a defrost cycle is required to remove frost build up from the second evaporator coil 152, the controller 50 actuates the three-way valve 28 to direct refrigerant 40 to only the first evaporator 32 at step 220. In this regard, the controller 50 continues to operate the first evaporator 32 at step 222 to continue cooling the interior 18 of the cabinet 12 while the second evaporator 34 is defrosted. Next, the controller 50 stops operation of the second evaporator fan 70 at step 224. The controller 50 then closes the third and fourth dampers 72, 74 (i.e., the second damper assembly) at step 226 to thermally isolate the second evaporator compartment 82 from the refrigerated portion 84 of the cabinet 12. These steps stop refrigerant flow through the second evaporator 34 and also stop air flow through the second evaporator 34. With the second evaporator compartment 82 thermally isolated from the remainder of the cabinet 12, the controller 50 starts operation of the second defrost heater 154 at step 228. The second defrost heater 154 warms the second evaporator 34 and the second evaporator coil 152 to melt frost and cause the moisture to drip onto the second drip pan 156 for removal from the second evaporator 34. The operational state of the refrigerator 10 at this point is shown in FIG. 7A.

One of the sensors S₇ connected to the second evaporator 34 may be configured to measure the temperature of the second evaporator 34. Thus, once the controller 50 determines that the second evaporator 34 has been heated to a first target temperature above the freezing point of water (0° C.) for a sufficient time to melt frost build up on the second evaporator coil 152, the controller 50 stops the second defrost heater 154 at step 230 and allows for a set period of “drip time” in which additional moisture drips off the second evaporator coil 152 into the second drip pan 156. In one example, this first target temperature may be about 10° C. After this “drip time” has occurred, the controller 50 directs refrigerant 40 with the three-way valve 28 through both of the first and second evaporators 32, 34 again at step 232, thereby cooling the second evaporator compartment 82. The second evaporator 34 may then be used as normally shown in FIG. 7B by opening the third and fourth dampers 72, 74 and starting the second evaporator fan 70. As a result of the second evaporator cover 78, the defrost cycle advantageously does not cause a significant temperature spike within the refrigerated interior 18 of the cabinet 12.

Furthermore, the dual evaporator 32, 34 arrangement is also advantageous during initial cool down of the cabinet 12 or immediately after the door 16 is opened. In this regard, the controller 50 is also operable to command the refrigerator 10 to perform an increased cooling cycle in these circumstances. In this increased cooling cycle, the controller 50 directs the three-way valve 28 to direct refrigerant 40 through both of the first and second evaporators 32, 34. The controller 50 also actuates the opening of the first, second, third, and fourth dampers 66, 68, 72, 74 such that heat is removed from the refrigerated interior 18 of the cabinet 12 by both evaporators 32, 34 simultaneously. This process advantageously and rapidly returns the refrigerated interior 18 to the intended cold storage temperature when the refrigerator 10 is initially started or immediately after a door 16 opening.

As briefly noted above, in one alternative embodiment the defrost cycle will be an adaptive defrost cycle selectively actuated at steps 202 and 218 of the method 200. In this adaptive defrost cycle, the period between defrost cycles and the time duration of the defrost cycles are modified based on a plurality of operational parameters monitored by the controller 50. For example, the conventional time-based defrost cycle may operate the first and second defrost heaters 144, 154 (not simultaneously) for 10 minutes every six hours. By contrast, the adaptive defrost cycle may monitor the actual temperature being maintained in the cabinet 12, as well as the number of door openings and amount of total time the door 16 is open. These and other factors are considered to determine how long the period should be before the next defrost cycle is started, and also how long the first and second defrost heaters 144, 154 should be operated in the next defrost cycle. In this regard, if the door 16 of the cabinet 12 is not opened often during a six hour period and the first and/or second evaporators 32, 34 are having little trouble maintaining the desired temperature within the refrigerated portion 84, then the next defrost cycle may be delayed by an additional number of hours and/or shortened in duration. Thus, the adaptive defrost cycle is highly energy efficient because the first and second evaporator coils 142, 152 are only defrosted when that cycle becomes necessary. Moreover, the adaptive defrost cycle automatically adjusts the refrigerator 10 for proper and efficient operation in a variety of environmental conditions.

While the present invention has been illustrated by a description of an exemplary embodiment and while this embodiment has been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept. 

What is claimed is:
 1. A refrigerator, comprising: a cabinet having a unitary refrigerated interior; a refrigeration fluid circuit for circulating a refrigerant, the refrigeration fluid circuit including a compressor, a condenser, an expansion device, a first evaporator located within the cabinet, a second evaporator located within the cabinet, and a three-way valve enabling selective communication of the refrigerant through one or both of the first and second evaporators; the first evaporator including a first evaporator coil, a first evaporator fan producing air flow through the first evaporator coil, and a first evaporator cover separating a first evaporator compartment from the refrigerated interior; the second evaporator including a second evaporator coil, a second evaporator fan producing air flow through the second evaporator coil, and a second evaporator cover separating a second evaporator compartment from the refrigerated interior; at least one first damper that may open to permit air circulation through the first evaporator cover from the refrigerated interior through the first evaporator; and at least one second damper that may open to permit air circulation through the second evaporator cover from the refrigerated interior through the second evaporator, wherein the three-way valve directs refrigerant into only one of the first and second evaporators when the other evaporator requires defrosting.
 2. The refrigerator of claim 1, wherein the first evaporator includes a first defrost heater, and the refrigerator further comprises: a controller operable to command the refrigerator to perform the following steps when the first evaporator requires defrosting: direct refrigerant with the three-way valve through only the second evaporator; remove heat from the refrigerated interior with the second evaporator; stop operation of the first evaporator fan; close the at least one first damper to isolate the first evaporator from the refrigerated interior; and start operation of the first defrost heater.
 3. The refrigerator of claim 2, wherein the second evaporator includes a second defrost heater, and the controller is further operable to command the refrigerator to perform the following steps when the second evaporator requires defrosting: direct refrigerant with the three-way valve through only the first evaporator; remove heat from the refrigerated interior with the first evaporator; stop operation of the second evaporator fan; close the at least one second damper to isolate the second evaporator from the refrigerated interior; and start operation of the second defrost heater.
 4. The refrigerator of claim 3, wherein the controller is further operable to command the refrigerator to perform the following steps during an initial cooling of the refrigerated interior or immediately after the cabinet is opened: direct refrigerant with the three-way valve through both of the first and second evaporators; and remove heat from the refrigerated interior with both of the first evaporator and the second evaporator simultaneously.
 5. The refrigerator of claim 3, wherein the controller is operable to modify an amount of time between defrost cycles and to modify an amount of time the first or second defrost heater is operating during a defrost cycle based on at least one measurable operating parameter.
 6. The refrigerator of claim 1, further comprising: a controller operable to command the refrigerator to perform the following steps during an initial cooling of the refrigerated interior or immediately after the cabinet is opened: direct refrigerant with the three-way valve through both of the first and second evaporators; and remove heat from the refrigerated interior with both of the first evaporator and the second evaporator simultaneously.
 7. The refrigerator of claim 1, wherein the expansion device includes at least one of a capillary tube or a valve.
 8. The refrigerator of claim 7, wherein the expansion device includes a first capillary tube disposed between the three-way valve and the first evaporator, and a second capillary tube disposed between the three-way valve and the second evaporator.
 9. The refrigerator of claim 1, wherein the refrigeration fluid circuit further includes an accumulator operatively connected to the first and second evaporators and the compressor.
 10. The refrigerator of claim 1, wherein the refrigeration fluid circuit further includes a filter/dryer operatively connected to the condenser and the expansion device.
 11. The refrigerator of claim 1, wherein the at least one first damper includes two first damper portions, one of the first damper portions in an open position permitting air flow into the first evaporator from the refrigerated interior, the other first damper portion in an open position permitting air flow from the first evaporator into the refrigerated interior.
 12. The refrigerator of claim 11, wherein the at least one second damper includes two second damper portions, one of the second damper portions in an open position permitting air flow into the second evaporator from the refrigerated interior, the other second damper portion in an open position permitting air flow from the second evaporator into the refrigerated interior.
 13. The refrigerator of claim 1, wherein the first and second evaporator compartments are adjacent and are separated by a divider wall.
 14. The refrigerator of claim 1, wherein each of the first and second evaporator covers includes a plurality of insulated panels.
 15. A method of operating a refrigerator including a cabinet having a unitary refrigerated interior; a refrigeration fluid circuit including a compressor, a condenser, a first evaporator located within the cabinet and having a first evaporator fan and a first defrost heater, a second evaporator located within the cabinet and having a second evaporator fan and a second defrost heater, and a three-way valve enabling selective communication of a refrigerant between the compressor/condenser and one or both of the first and second evaporators; at least one first damper configured to isolate the first evaporator from the refrigerated interior; and at least one second damper configured to isolate the second evaporator from the refrigerated interior, and the method comprises: when the first evaporator requires defrosting, directing refrigerant with the three-way valve through only the second evaporator; removing heat from the refrigerated interior with the second evaporator; stopping operation of the first evaporator fan; closing the at least one first damper to isolate the first evaporator from the refrigerated interior; and starting operation of the first defrost heater.
 16. The method of claim 15, further comprising: when the second evaporator requires defrosting, directing refrigerant with the three-way valve through only the first evaporator; removing heat from the refrigerated interior with the first evaporator; stopping operation of the second evaporator fan; closing the at least one second damper to isolate the second evaporator from the refrigerated interior; and starting operation of the second defrost heater.
 17. The method of claim 16, further comprising: during initial cool down of the refrigerated interior or immediately after the cabinet is opened, directing refrigerant with the three-way valve through both of the first and second evaporators; and removing heat from the refrigerated interior with both of the first evaporator and the second evaporator simultaneously. 